In image scan devices, such as contact image sensor (CIS) image scan devices, typically, a scan head is moved along a platen by an automatic drive system to scan an image of a flat object that is supported by the platen. The CIS needs to maintain a close and constant scanning distance with respect to the object to be able to make a scan of relative quality. The scan device has a cover that presses the document against the platen when closed. The scan head is biased against the platen while moving along the platen to maintain the constant distance with respect to the platen. Typically, a compression bias spring is used to bias the scan head against the platen. The compression spring is biased against the bottom of the scan head, between the carriage and the scan head, to push the scan head against the platen. The scan head has wheels that engage the platen and guide the CIS at a constant small distance along the platen.